so i have an 07 grizzly 450 and it has started backfireing quite a bit now, and bad. if im riding at full throttle, sometimes itll just die down and then go kaabooom!!! then i can go again. anyone know how to fix this?

 

first off.........ouch......., umm could be electrical, timing, if it's carbed, maybe that....did you get it new? used?....when you start it, and it idles does it backfire? or does it only back fire when you start riding it?....you have to give more info man.

 

alright, i got it brand new, however, its a lemon haha. ive taken it in probably 6 times to get it fixed. and when it idles, its kinda funny like it doesnt stay steady, almost like the idle is set to low but if i ride it for a bit and then try to shift, it doesnt shift because the idle is to high and the clutch just kinda slips. anyways, it usually happens when im either deacelerating or when im riding it

 

So let me see if I got this correct. Its only on let off that it backfires....or is it at wot that it backfires?
If its on let off, its a real common issue. The idle circuit is too lean. There are many reasons for lean, but most likely its due to using blended fuel(alcohol added). Is everything totally stock?

This comes from the mikuni carb website

4: Backfires in Exhaust

Note:

It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.

The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers.

Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires.



Other possible causes:

Air Leaks:

Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust backfiring. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system backfiring.

A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction.

Lean Carburetion:

While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit.

Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping. The procedure for adjusting the pilot circuit is covered in the Tuning Manual.

Ignition:

If exhaust system popping is very loud, irregular and accompanied by loss of power, then you should suspect that the ignition system is not performing as it should. If, for some reason, the ignition sometimes fires at the wrong time, then exhaust popping can become very energetic (loud). Look for failing high tension leads (plug wires), failing ignition coil(s) and especially switches or connectors as possible causes.

Most likely a little turn richer, 1/4 turn or so, on the mixture screw will cure it, if everything is stock, and otherwise working correctly.

 

thank you for that help, looks like the ignition is the one for me. now i just need to find out whee the mixture screw is

 

The Ignition is fine. The mixture screw is on the underside of the carb, just forward of the float bowl

 

ok thanks, thisll be a pain to get to, ill probably look at it later